1. Field of the Invention
The present invention relates to a backlight unit of a liquid crystal display (LCD) device, and more particularly, to a light emitting diode (LED) lamp unit, to obtain a thin profile, to improve the uniformity of light, and to simplify the power connection line for the operation of the device.
2. Discussion of the Related
In general, cathode ray tubes (CRTs), which are one type of display device, have been widely used as monitors for televisions, measuring apparatuses, and information terminals. However, the CRT cannot satisfy the demand for compact size and light weight devices due to the size and weight of the CRT itself. Thus, various display devices, such as liquid crystal display (LCD) devices that use the electric field optical effect, plasma display panels (PDP) using a gas discharge, and electroluminescence display (ELD) devices using an electric field luminous effect, have been studied to substitute the CRT.
Among the display devices, the LCD device has been extensively researched, so that the LCD device having low power consumption, slim size and light weight is in active development and production as monitors for desktop computers (or personal computers) and large sized display devices, as well as laptop computers (or notebook computers). Accordingly, LCD devices are popular. Most LCD devices control the light transmittance of ambient light to display an image. In this respect, it is often necessary to provide an additional light source, such as a backlight unit, to emit light to the LCD panel of the LCD device.
The backlight unit is generally used to read information displayed on a screen of the LCD device in dark surroundings. Backlight units often have a thin light-guiding plate because of the demand for good design, low power consumption, and thin profile. Also, there are research to further develop the function of representing various colors and of improving the display grade by using a light emitting diodes (LED) are ongoing.
Generally, the LED is a solid device using the photoelectric conversion characteristics of a semiconductor, and more particularly the LED is a semiconductor device of emitting light when a forward voltage is applied thereto. In comparison to a lamp of using tungsten filaments, the LED emits light at a lower voltage. Lamps using tungsten filaments emit light by heating the filaments. Meanwhile, the LED emits light with the energy difference generated by the recombination of electrons and holes. Accordingly, the LED is in widespread use for various display devices.
When an A.C. voltage of several values is applied to the LED, the LED emits light. With an LED, there is no requirement for providing a DC-AC converter to a driving unit, whereby the driving unit has a simplified structure. Also, since the LED is the semiconductor device, the LED has high reliability, compact size and long lifespan as compared with the CRT.
Hereinafter, a general LED lamp, which can be used for a light-emitting device by itself or for a light source of a display device will be described with reference to the accompanying drawings.
FIG. 1A is a photograph of a general LED lamp unit. FIG. 1B is a cross sectional view of a general LED lamp unit. FIG. 2 illustrates a progressing path of light emitted from an LED lamp of FIG. 1A and FIG. 1B. FIG. 3A illustrates rectangular coordinates of the relative intensity characteristics of light by an angular degree of a general LED lamp unit. FIG. 3B illustrates polar coordinates of the relative intensity characteristics of light by an angular degree of a general LED lamp unit.
As illustrated in FIG. 1A and FIG. 1B, the general LED lamp unit includes an LED chip 10, a bullet-shaped optical lens 13, cathode and anode lead wires 14 and 15, and a reflecting curve 11. The bullet-shaped optical lens 13 covers the LED chip 10, and the cathode and anode lead wires 14 and 15 are connected with both ends of the LED chip 10. Also, the reflecting curve 11 covers the side of the LED chip 10. Herein, a non-explained reference number 12 is a wire for connecting the LED chip 10 with the cathode lead wire 14 and the anode lead wire 15.
With an LED lamp having the aforementioned structure, the light emitted from the LED chip 10 is mostly concentrated on the optical lens 13, whereby the light is progressing to the vertical direction, as illustrated in FIG. 2.
In FIG. 3A and FIG. 3B, it illustrates the relative intensity characteristics of light by an angular degree of the general LED panel. As illustrated in FIG. 3A and FIG. 3B, the light emitted from the LED chip 10 is mostly progressing to the vertical direction. In this case, the light emitted from the LED lamp is concentrated on and is progressing to one direction (vertical direction). Accordingly, it is impossible to apply the LED lamp unit to the backlight unit of requiring the uniformity of light on the entire area. In order to apply the LED lamp unit to the backlight unit, it is necessary to provide a plurality of LED lamps. In addition, the LED lamp unit requires additional optical elements for scattering the light emitted from the LED lamp.
Hereinafter, a related art LED lamp unit having an improved structure, for solving the problem of the general LED lamp in which the light is concentrated in vertical, will be described as follows.
FIG. 4 is a schematic view of an LED lamp unit according to the related art. FIG. 5 is a perspective view of an optical lens of an LED lamp unit of FIG. 4 according to the related art. FIG. 6 illustrates a relative intensity according to an angular degree of an LED lamp unit of FIG. 4.
As illustrated in FIG. 4 and FIG. 5, a related art LED lamp 40 includes a mortar-shaped optical lens 50 and an LED chip (not illustrated), wherein the mortar-shaped optical lens 50 is suitable for a side emitting type, and the LED chip is positioned inside the mortar-shaped optical lens 50.
Referring to FIG. 6, the light emitted from the LED chip is progressing to the side direction through the optical lens 50 since the optical lens 50 is formed in shape of mortar. Accordingly, in case the related art LED lamp unit is applied to the backlight unit, it is possible to obtain the great luminance with the smaller number of the LED lamps, as compared with the number of the LED lamps in case of using the general LED lamp unit.
However, the related art LED lamp unit has the following disadvantages.
First, with a related art LED lamp unit, the light emitted from the LED lamp is progressing to the side direction since the optical lens is formed in shape of mortar. However, it is impossible to obtain the thin profile due to the thickness of the optical lens.
Also, the upper edge of the optical lens is thin, so that the upper edge of the optical lens may be easily damaged due to the external force. Also, in case the optical lens is heavily damaged, the characteristics of light emitted from the LED lamp may be changed.